This application claims the priority of Korean Patent Application No. 2002-10389 filed on 27 Feb. 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a fan and shroud assembly, and more particularly, to a fan and shroud assembly in which swirl prevention units are arranged at an airflow inlet of a shroud where a fan is inserted so that swirling of airflow generated during airflow by rotation of the fan is reduced and thus air can be blown with effectively lowered noise.
2. Description of the Related Art
As shown in FIG. 12, a fan 10 used for cooling of a heat exchange medium passing the inside of a heat exchanger such as radiator or condenser of a car includes a hub 11 coupled to a shaft of a driving source such as a motor, and a plurality of blades 12 radially arranged along the outer circumference surface of the hub 11. A fan band 13 connecting end tips of blades 12 can be further provided to prevent deformation of the blades 12. Thus, as the fan 10 rotates by a rotating force transferred from the driving source to the hub 11, air can be blown by the blades 12 in an axial direction. A shroud may be fixed to a heat exchanger to effectively guide the air blown by the fan 10 toward the heat exchanger. The shroud may have an airflow inlet sized to insert the fan 10 to be rotated therein to guide airflow and be formed to support the motor as a driving source.
Here, the shroud constituting a puller type fan shroud assembly which is installed, for example, at the rear of the heat exchanger to suck air and to blow the air to the rear of the heat exchanger will be described below. Referring to FIGS. 10 and 11, a shroud 20 includes a housing 21 into which the fan 10 can be rotatably inserted and having an airflow inlet 22 to guide the flow of air by the fan 10, a motor support ring 23 provided at the center of the airflow inlet 22, and a plurality of guide ribs 24 radially arranged while connecting the housing 21 and the motor support ring 23 to support the motor support ring 23.
The airflow inlet 22 is formed by an outer guide ring 25 protruding to the rear of the housing 21. For a smooth airflow, a bell mouth 26 is formed at the rear end of the outer guide ring 25 bent inwardly and an inner guide ring 27 can be extended to the front side from an inner end portion of the bell mouth 26. The fan 10 is installed to have a predetermined gap with the inner guide ring 27 at a position where the fan band 13 (the end tips of the blades 12 when the fan band 13 is not present) corresponds to the rear end of the bell mouth 26. The leading end of the fan band 13 is extended toward the outer guide ring 25 and encompasses the leading end of the inner guide ring 27 for a smooth airflow.
The above structure of the airflow inlet 22 and the fan band 13 has been suggested to minimize generation of noise by reducing the generation of air swirling at the end portion of the blades 12 during rotation of the fan 13. However, air actually comes through a gap between the outer guide ring 25 and the outer circumferential surface of the fan band 13 so that air swirling occurs in a space between the outer guide ring 25 and the inner guide ring 27 and flows reversely to the airflow direction. Thus, the amount of airflow is lost due to the reverse airflow and noise is generated due to the air swirling.
In the meantime, U.S. Pat. No. 6,254,343 discloses a low noise cooling fan. In the cooling fan, a housing where a rotor having a plurality of fan blades is installed has a path connecting a first end portion forming an inlet and a second end portion forming an outlet. The inlet has a sectional area greater than the path. A transitional area connecting the inlet and the path and the inlet define a steep step. Also, the inlet has an inner side surface parallel to a passage for fluid and a plurality of protrusions are formed on the inner side surface.
In the above cooling fan, although air suction noise at an edge of the inlet is reduced by the step and the protrusions, noise generated due to swirl at the end tips of the fan blades cannot be reduced. That is, since air swirling is generated between the end tips of the fan blades and the inner circumferential surface of the path by the rotation of the end tips of the fan blades constituting the rotor, noise is generated greatly and further an efficiency of airflow is deteriorated.
Also, U.S. Pat. No. 5,489,186 discloses a fan and housing assembly where a plurality of vanes are installed at a gap between a housing and a fan band and a reversing airflow is controlled by the vanes.
However, in the above fan and housing assembly, although the reverse airflow from the downstream at a high pressure to the upstream at a lower pressure can be controlled, since the vanes made of a thin member are arranged at an identical interval and protrude toward a path of the housing, air swirling generated in the same direction as a direction in which a fan rotates cannot be effectively prevented. Accordingly, a noise reduction effect cannot be greatly improved.